The Ames Salmonella/microsome strains TA-100 and TA-1535 are being used to test for the mutagenicity of Tris, a known carcinogen, and some of its metabolites. The chemical structures of a series of metabolites were determined and the metabolites were synthesized at NIEHS. A gradient of mutagenic responses was seen when the metabolites were tested. These responses ranged from very weakly positive to as mutagenic as the parent compound Tris. All positive responses required Aroclor-induced rat liver S-9.